<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <style>
   
  </style>
</head>

<body>
  <div id="app">
    <input type="text" v-model="firstName">
    <input type="text" v-model="lastName">
    =>
    {{ fullName }}
  </div>
  <script src="./vue.js"></script>
  <script>
    const vm = new Vue({
      el: '#app',
      data: {
        firstName:"",
        lastName:""
      },
      methods: {
      },
      computed:{
        fullName(){
          return this.firstName+'.'+this.lastName
        }
      }
    })
  </script>
</body>

</html>